An IP multimedia subsystem (IMS) is defined for a wideband code division multiple access (WCDMA) network by the Third Generation Partnership Project (3GPP) in the R5/R6 standard. The IMS implements packet voice and data services in third generation (3G) mobile networks and provides unified multimedia services and applications. The IMS uses an IP packet domain as its bearer channel for control signaling and media transmission and uses the Session Initiation Protocol (SIP) for exchanging call control signaling. In the IMS, the user subscription data is centralized on a home subscriber server (HSS) for management. Services are uniformly provided by an application server (AS) and session control is completed by a call session control function (CSCF). In the network structure, the service provision is completely separated from the session control. A serving CSCF (S-CSCF) triggers services to the AS for processing. Multiple ASs may process services together. A user accesses the IMS through its current proxy CSCF (P-CSCF) and sessions and services are controlled by the serving node in the home domain of the place where the user is registered. Thus, the user may enjoy the same services at different access points. This separates service management, session control, and bearer access from each other, and provides services independent of access and location.
The IMS is defined in 3GPP and Telecommunications and Internet Converged Services and Protocols for Advanced Networking (TISPAN) standards. In 3GPP2 standards, a multimedia domain (MMD) similar to a multimedia subsystem is defined. The structure of the MMD is similar to the structure of the IMS. To simplify descriptions, the following describes only the IMS, but apparently, the methods hereunder are also applicable to the MMD.
In the evolution to IMS networks, circuit switched (CS) networks and IMS networks may coexist for a period of time. In this case, operators want to have a control point to control the services in the CS and IMS domains in a centralized way so as to decrease the deployment and management cost and to provide a consistent service experience. The control point is usually deployed in the IMS network and is implemented by the AS. That is, when a user accesses through a CS network, the IMS network also provides services for the user.
This issue also exists in an IMS centralized service (ICS) in 3GPP and TISPAN standards. FIG. 1 shows the structure of the ICS. As a new function, the local-CS access adaptation function-network (L-CAAF-n) may be independently deployed between a user equipment (UE) and a mobile switching center (MSC) or be integrated with the MSC. The L-CAAF-n is mainly adapted to identify whether a user is an ICS user. If the user is an ICS user, the L-CAAF-n performs mutual transformation on CS signaling and SIP signaling of the user and sends the transformed signaling to an IMS CS control function (ICCF). The L-CAAF-n may be regarded as an access adapting unit that transforms CS signaling into SIP signaling. The ICCF is an AS with the user agent (UA) function, and accesses the IMS domain as an agent of a UE in the IMS domain. When an ICS user accesses through the CS domain, the L-CAAF-n needs to send the transformed SIP signaling to the ICCF and the ICCF accesses the IMS domain as an agent of the user. The ICCF controls the access of the user to the IMS domain through the CS domain.
During the implementation of the present invention, the inventor discovers at least the following problems in the prior art:
Different ICS users may have different ICCFs. When an ICS user is routed to an L-CAAF-n for the first time, the L-CAAF-n does not have the ICCF address information of the user and fails to send the transformed SIP signaling to the ICCF. Thus, it is urgent to enable the L-CAAF-n to acquire the address information of the ICCF and determine whether a user is an ICS user.